Prolonged Preservation Of The Heart Prior To

Transplantation Essay, Research Paper

Biochemistry

Prolonged Preservation of the Heart Prior to Transplantation

Picture this. A man is involved in a severe car crash in

Florida which has left him brain-dead with no hope for any

kind of recovery. The majority of his vital organs are

still functional and the man has designated that his organs

be donated to a needy person upon his untimely death.

Meanwhile, upon checking with the donor registry board, it

is discovered that the best match for receiving the heart of

the Florida man is a male in Oregon who is in desperate need

of a heart transplant. Without the transplant, the man will

most certainly die within 48 hours. The second man’s

tissues match up perfectly with the brain-dead man’s in

Florida. This seems like an excellent opportunity for a

heart transplant. However, a transplant is currently not a

viable option for the Oregon man since he is separated by

such a vast geographic distance from the organ. Scientists

and doctors are currently only able to keep a donor heart

viable for four hours before the tissues become irreversibly

damaged. Because of this preservation restriction, the

donor heart is ultimately given to someone whose tissues do

not match up as well, so there is a greatly increased chance

for rejection of the organ by the recipient. As far as the

man in Oregon goes, he will probably not receive a donor

heart before his own expires.

Currently, when a heart is being prepared for

transplantation, it is simply submerged in an isotonic

saline ice bath in an attempt to stop all metabolic activity

of that heart. This cold submersion technique is adequate

for only four hours. However, if the heart is perfused with

the proper media, it can remain viable for up to 24 hours.

The technique of perfusion is based on intrinsically simple

principles. What occurs is a physician carefully excises

the heart from the donor. He then accurately trims the

vessels of the heart so they can be easily attached to the

perfusion apparatus. After trimming, a cannula is inserted

into the superior vena cava. Through this cannula, the

preservation media can be pumped in.

What if this scenario were different. What if doctors were

able to preserve the donor heart and keep it viable outside

the body for up to 24 hours instead of only four hours. If

this were possible, the heart in Florida could have been

transported across the country to Oregon where the perfect

recipient waited. The biochemical composition of the

preservation media for hearts during the transplant delay is

drastically important for prolonging the viability of the

organ. If a media can be developed that could preserve the

heart for longer periods of time, many lives could be saved

as a result.

Another benefit of this increase in time is that it would

allow doctors the time to better prepare themselves for the

lengthy operation. The accidents that render people

brain-dead often occur at night or in the early morning.

Presently, as soon as a donor organ becomes available,

doctors must immediately go to work at transplanting it.

This extremely intricate and intense operation takes a long

time to complete. If the transplanting doctor is exhausted

from working a long day, the increase in duration would

allow him enough time to get some much needed rest so he can

perform the operation under the best possible circumstances.

Experiments have been conducted that studied the effects of

preserving excised hearts by adding several compounds to the

media in which the organ is being stored. The most

successful of these compounds are pyruvate and a pyruvate

containing compound known as

perfluoroperhydrophenanthrene-egg yolk phospholipid

(APE-LM). It was determined that adding pyruvate to the

media improved postpreservation cardiac function while

adding glucose had little or no effect. To test the

function of these two intermediates, rabbit hearts were

excised and preserved for an average of 24.5 1 0.2 hours on

a preservation apparatus before they were transplanted back

into a recipient rabbit. While attached to the preservation

apparatus, samples of the media output of the heart were

taken every 2 hours and were assayed for their content. If

the compound in the media showed up in large amounts in the

assay, it could be concluded that the compound was not

metabolized by the heart. If little or none of the compound

placed in the media appeared in the assay, it could be

concluded that compound was used up by the heart metabolism.

The hearts that were given pyruvate in their media

completely consumed the available substrate and were able to

function at a nearly normal capacity once they were

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